Colicin K

Colicin K is a type of Colicin, a bacteriocin made by E. coli which acts against other nearby E. coli to kill them by forming a pore in the membrane, leading to depolarisation of the membrane which kills the cell.

Synthesis and release
The colicin K operon is encoded on a plasmid in the E. coli cell. The operon encodes the colicin itself, its Colicin Immunity Protein and a protein for release of the colicin into the surrounding area. The immunity protein acts by inserting into the membrane of the colicin-producing cell, and prevents the colicin from forming a pore in the membrane.

Mechanism of uptake
The receptor binding domain of Colicin K binds to the outer membrane protein Tsx of the target cell, a constitutively expressed protein parasitised by the colicin. The translocation domain then recruits proteins from the Tol family to translocate across the membrane and into the cytoplasm, through a mechanism as yet unidentified.

Killing Activities
The cytotoxic domain forms a pore in the membrane of the target cell, causing it to depolarise. This prevents the cell from being able to synthesise ATP, ultimately leading to the death of the cell.